– movingcoilmetersrespondtobothpositiveandnegativevoltages,each producing deflections in opposite directions– asymmetricalalternatingwaveformwillproducezerodeflection(the mean value of the waveform)– therefore we use a Rectifier to produce a unidirectional signal– meter then displays the Average value of the waveform– metersareoftencalibratedtodirectlydisplayR.M.S.ofsinewaves all readings are multiplied by 1.11 – the form factor for a sine wave– asaresultwaveformsofotherformswillgiveincorrectreadings for example when measuring a square wave (for which the form factor is 1.0, the meter will read 11% too high)